1. Field of the Invention
The present invention relates generally to correcting methods and correcting apparatuses, and more particularly to a correcting method and a correcting apparatus that correct a coordinate value detected by a detecting pin.
2. Description of the Related Art
A machining apparatus known in the related art uses, for example, a microcomputer to carry out numerical control in three-dimensionally machining a work in accordance with predetermined data. Such a machining apparatus includes: a spindle equipped with a tool; and a holder to hold a work. The machining apparatus three-dimensionally changes the relative positions of the tool-equipped spindle and the work in machining the work with the tool, thus forming the work into a desired shape.
Positioning of target components of a machining apparatus, such as a spindle and a holder, is effected at a predetermined time, such as at the time of shipment from a factory or parts replacement. Such a positioning process involves: acquiring a coordinate value of a measurement point preset for positioning; and calculating a correction value for positioning from the acquired coordinate value and a previously stored measurement point coordinate value. The correction value will hereinafter be referred to as a “positioning correction value” when appropriate. The target components are positioned in accordance with the positioning correction value calculated.
The measurement point coordinate value is acquired using a detecting pin mounted on the spindle. The machining apparatus acquires the coordinate value of a spot where the detecting pin has come into contact with the measurement point.
Unfortunately, the detecting pin may be obliquely mounted on the spindle, which causes the shaft of the detecting pin to get out of alignment. A measurement point detected by such a detecting pin results in an inaccurate measurement point coordinate value, unlike a measurement point detected by a detecting pin properly mounted on the spindle (i.e., a detecting pin whose shaft extends vertically). Thus, the use of a positioning correction value calculated from the inaccurate measurement point coordinate value will disadvantageously not enable proper positioning of the target components.
To solve such a problem, a known method involves calculating a correction value to correct a coordinate value detected by a detecting pin whose shaft is out of alignment. The correction value calculated will hereinafter be referred to as a “shaft misalignment correction value” when appropriate. The known method further involves correcting a coordinate value of a measurement point using the shaft misalignment correction value, and then calculating a positioning correction value using the measurement point coordinate value corrected.
In acquiring the shaft misalignment correction value, a spindle is first moved such that a detecting pin comes into contact with a detection point set in advance for shaft misalignment correction value calculation, thus acquiring a coordinate value of the detection point. Subsequently, the spindle is rotated around the Z axis so as to rotate the detecting pin by 180 degrees. The spindle in this state is moved such that the detecting pin comes into contact with the detection point again, thus acquiring a coordinate value of the detection point. From the two coordinate values acquired, the shaft misalignment correction value is calculated. Using the shaft misalignment correction value calculated, the measurement point coordinate value is corrected.
The upper and lower ends of the detecting pin whose shaft is out of alignment, however, have different degrees of misalignment unlike the upper and lower ends of a detecting pin whose shaft is in alignment. The degree of misalignment of the detecting pin whose shaft is out of alignment increases as the detecting pin extends to its lower end (or its tip). Suppose that the position of contact of the detecting pin with the detection point when the detection point is detected and the position of contact of the detecting pin with the measurement point when the measurement point is detected are different in the up-down direction. In this case, the measurement point coordinate value will not be corrected properly, resulting in improper positioning of target components. In view of the foregoing, there is a need for a correcting method and a correcting apparatus that enable a coordinate value detected by a detecting pin to be corrected more properly than before.